Commutator shorting device for motors



Sept. 6, 1932 "o 1,876,235

COMMUTATOR SHORTING DEVICE FOR MOTORS Filed Sept. 17, 1930 2 Sheets-Sheet 1 IN V: NTOR: 771 TSuJ/RO 1'0 7- 8, v 3% sflpt. 6, 1932. Q 1,876,235

COHMUTATOR SHORTING DEVICE FOR MOTORS Filed Sept. 17. 1930 2 Sheets-Sheet 2 Patented Sept. 6, 1932 UNITED STATES PATENT OFFICE TATSUJIRO 110, OF MEGURO MACHI, EBARA GUN, TOKYO FU, JAPAN, ASSIGNOR TO 'TOA DENKI KABUSHIKI KAISHA, OF SHIIBUYA MACHI, TOYOTAMA GUN, TOKYO FU,

JAPAN, A CORPORATION OF JAPAN COMMUTATOB SHORTING DEVICE FOR MOTORS Application filed September 17, 1930. Serial No. 482,525.

This invention relates to a device for short circuiting -commutators of electric motors. Certain types of electric motors, as is well known by those skilled in the art, requires a commutator for startingthe motors under load, and as soon as the motor armature or rotor has nearly reached running speed, such commutator should be short circuited to obtain efficient operation under normal running in conditions. Some such mechanism is generally used in repulsion starting and other similar types of motors.

As such commutators must be made up of many segments and each completely shorted I to every other segment, there are many con tacts to be made, because of which it has hitherto been difiicult to accomplish this end and many means have been tried, most of which are both complicated and costly. As

an by far the largest field of usefulness of such motors is in the small sizes, Where first cost of course is of great importance, costly complicated mechanisms are very undesirable.

In the drawings,

Fig. 1 is a partly sectional side elevation of a commutator embodying the features of the present invention;

Fig. 2 is an end view thereof;

Fig. 3 is a View similar to Fig. 2, but illustrating a modified form of the invention;

Fig. 4 is a perspective view illustrating one form of the straps constituting a part of the improved short-circuiting device; and

Figs. 5 and 6 are perspective views respectively of modified forms of straps.

Referring to the drawings, and particularly to Figs. 1 and 2, the numeral 1 designates a commutator, in engagement with which are a pair of brushes 2 through which the current passes. The commutator is provided with a recess 3 extending around its periphery, and mounted on the commutator in encircling relation to said recess is a collar 7 said collar being insulated from the commutator by a gasket 11 of insulating material. Threaded into the collar 7 at diametrically opposite points are a pair of radially extending headed studs 12 on each of which is mounted for sliding movement a weight 5. A pair of 5 straps 4, 4, are disposed within the peripheral recess 3 of the commutator, each of said straps being in the form of a loop encircling the commutator for the greater part of its circumference, the opposite ends of the strap 4 passing through openings 7 a in the collar 7 and secured by screws 13 to opposite sides of one of the weights 5, while the ends of the strap 4 pass through similar openings 7 in the said collar and are secured. by screws 13 to opposite sides of the other weight 5. By this arrangement the straps 4 and 4 necessarily intersect each other in their passage around the commutator from opposite sides thereof, and for this reason, as shown clearly in Fig. 4, one of the straps, as for instance the strap 4, is provided at the proper points in its length with a pair of rectangular openings 14 through which the ends of the strap 4 pass, the latter strap being cut away to form narrow portions or necks 15 which are freely operable in said openings. One end of a coil spring 6 is attached to each of the screws 13 and 13, the opposite ends of said springs being connected to the ends of a pair of links 8, each provided with a centrally disposed elongated slot 10 through which passes loosely a headed screw 9 which is threaded into the collar 7. By this construction the spring tension is equalized.

' From the foregoing it will be obvious that upon rotation of the commutator at such speed as to impart to the weights sufficient centrifugal force to overcome the tension of the springs 6, the outward movement of the Weights will cause the straps 4 and 4 to engage the commutator after the manner of a brakeband. In Figs. 1, 2 and 3 the weights are shown in their outermost position, and the corresponding position of the straps is indicated in broken lines, and it will be noted that each strap is in contact with and will thus shortcircuit more than one-half of the total number of commutator segments. The relation between the weights 5 and the tension of the springs 6 is preferably so adjusted that the weights will operate when the speed of rotation is about ten per cent below the synchronous speed of the motor. When the speed of rotation is reduced, the weights 5 are caused to move inward under the tension of the springs 6, thus carrying the straps 4, 4* out of contact with the commutator and into abutting relation with the inner periphery of the collar 7, said collar being disposed at the proper distance from the commutator to maintain the straps in their inoperative position at a uniform distance from the commutator.

Fig. 3 illustrates a slightly different form of the invention. In the device shown in this figure a single strap l" is used, said strap completely encircling the commutator and having its opposite ends secured to weights 5 at opposite sides of the commutator. The strap in this instance may be of the form shown in Fig. 5, wherein the strap is provided near one end with a rectangular opening 16 and near its opposite end with a narrow portion or neck 17 movable within said opening to permit contraction and expansion of the strap around the commutator. In place of the strap at, however, a simple wire strap such as the strap & shown in Fig. 6 may be used.

The straps herein described are made of material such as phosphor bronze that is a good electrical conductor and flexible. The strap may be flat, round, square, rectangular or in the case of large motors it may be braided from strands of suitable material.

This commutator shorting device is very simple in construction, consists of few parts and will seldom get out of order. Being inexpensive it is a distinct improvement over the known methods.

The method of operation is such that all of the commutator segments 1 are completely and simultaneously short-circuited, thereby preventing injurious arcing and insuring long life of the contracting members. This is accomplished as follows. The springs 6 are under considerable initial tension, so that their tension changes very little whether the weights 5 are extended or at rest against the collar 7. On the other hand, when the centrifugal force of the weights 5 overcomes the spring tension, the weights begin to travel outward and the centrifugal force increases more rapidly than the spring tension increases so that they fly out almost instantly, giving a positive and a quick pull on the straps 4.

Another reason is that the straps being held close to and at a uniform distance from the commutator 1 the shorting of all segments takes place practically simultaneously.

The straps being flexible, make a firm contact with the commutator segments, being pulled taut from their ends, so that slight differences in the height of the segment will not prevent proper shorting of the adjacent segments, due to this flexibility.

I claim.

1. The combination with a rotatable commutator, of flexible straps disposed in encircling relation to said commutator and normally out of contact therewith, radially movable Weights mounted for rotation with the commutator and secured to said straps thereby under centrifugal force to carry the straps into contact with said commutator, and tension means for opposing the centrifugal movement of said weights.

2. The combination with a rotatable commutator, of flexible short-circuiting straps disposed in encircling relation to said commutator, weights secured to said straps and centrifugally operable upon rotation of the commutator to carry the straps into contact with said commutator, and tension means for opposing centrifugal motion of said weights and maintaining said straps normally out of contact with the commutator.

3. The combination with a rotatable commutator, of flexible short-circuiting straps disposed in encircling relation to said commutator, weights secured to said straps and centrifugally openble upon rotation of the commutator to carry the straps into contact with said commutator, tension means for opposing centrifugal motion of said weights and maintaining said straps normally out of contact with the commutator, and a circumferentially disposed stop member cooperating with said tension means to retain said straps at a uniform distance from said commutator.

4. The combination with a rotatable commutator, of a collar disposed in encircling relation to said commutator and spaced therefrom, short-circuiting straps disposed between the commutator and said collar, weights secured to said straps and centrifugally operable upon rotation of the commutator to carry the straps into contact with said commutator, and springs secured to said weights for opposing centrifugal movement thereof and maintaining said straps normally in contact with said collar and at a uniform distance from the commutator.

TATSUJIRO I10. 

